Optical modules including customizable spacers for focal length adjustment and/or reduction of tilt, and fabrication of the optical modules

ABSTRACT

An optical module comprising: a plurality of active optoelectronic components each one mounted on a respective printed circuit board (PCB), wherein each active optoelectronic component is associated with a respective different optical channel; a plurality of optical assemblies, each one is substantially aligned over a different respective optical channel; and a spacer separating the active optoelectronic components and PCBs from the optical assemblies, wherein the optical assemblies are attached by adhesive directly to an optical assembly-side surface of the spacer. A first active optoelectronic component is separated, by the spacer, from a first optical assembly by a first distance and a second active optoelectronic component is separated, by the spacer, from a second optical assembly by a different second distance. Also contemplated is a method for fabricating an optical module that comprises: modifying a height of one or more extensions on a spacer to adjust for at least one of a focal length or tilt of at least one optical channel.

FIELD OF THE DISCLOSURE

This disclosure relates to optical modules for image sensing devicessuch as cameras, and other devices. It also relates to methods ofmanufacturing such modules.

BACKGROUND

During the manufacture of devices, such as optical modules for arraycameras, manufacturing irregularities or manufacturing deviations mayoccur, for example, because of more or less unavoidable variations orinaccuracies in one or more of the process steps. For example, when theoptical devices include one or more passive optical elements such aslenses, the devices may have focal lengths that slightly vary one fromthe other despite having the same nominal focal length. In some cases,the focal length may correspond to the flange focal length (FFL), ormore generally, the focal length may refer to any focal length parameter(e.g., the effective focal length (EFL)). In any event, variations inthe focal lengths can result in the focal plane of the lens system lyingoff the image sensor plane, which can lead to inferior image quality.

Another problem that can arise, for example, in array cameras isshifting of the optical axes of the various optical channels as a resultof thermal expansion of the lens stacks. In some cases, thermalexpansion can cause the various optical channels to shift laterally withrespect to the image sensor plane. Thermal expansion also may cause theoptical channels to become tilted with respect to the desired opticalaxis. Thus, thermal expansion also can lead to inferior image quality.

Additional problems that can arise relate to the use of adhesive in theoptical assembly and/or tilt of the barrel lens or optical assembly. Forexample, a lens barrel or optical stack may be attached to a transparentwafer with adhesive, or an optical assembly may be attached to anothersubstrate (e.g., a printed circuit board (PCB) or image sensor) withadhesive. The adhesive must be applied with precision and accuracybecause uneven, unequal distribution of adhesive may cause tilt in thebarrel/lens stack or tilt in the optical assembly, which can result inreduced image quality. In addition, if not controlled properly, adhesivemay migrate to the active portion of the image sensor, which can resultin the optical modules being unusable.

SUMMARY

The present disclosure describes optical modules and methods offabricating the optical modules. Various approaches are described toprovide adjustments to reduce variations in the focal lengths of theoptical channels, to reduce the occurrence of tilt of the module'soptical channels, and/or prevent adhesive from migrating to activeportions of the image sensor.

For example, in one aspect, an optical module includes activeoptoelectronic components each of which is mounted on a respectiveprinted circuit board, wherein each of the active optoelectroniccomponents is associated with a respective different optical channel. Atransparent cover extends over the active optoelectronic components andis substantially transparent to one or more wavelengths of lightdetectable or emitted by the active optoelectronic components. Themodule includes beam shaping systems, each of which is associated with adifferent one of the optical channels and which is disposed over thetransparent cover. A spacer separates the active optoelectroniccomponents and printed circuit boards from the transparent cover. Afirst one of the active optoelectronic components is separated, by thespacer, from the transparent cover by a first distance, and a second oneof the active optoelectronic components is separated by the spacer fromthe transparent cover by a different second distance.

In some cases, the transparent cover is omitted. This can help reducethe overall height of the module, which can be important in someapplications.

Some implementations one or more of the following features. For example,the spacer can include first edge features attached to top surfaces ofthe active optoelectronic components and second edge features attachedto top surfaces of the printed circuit boards. The second edge featurescan be attached to the top surfaces of the printed circuit boards byadhesive. In some cases, the spacer is a single monolithic piece, andthe transparent cover has a substantially uniform thickness. The spacermay have trenches that provide space for electrical connections from theactive optoelectronic components to the printed circuit boards. Thetrenches also may provide space and protection for adhesive. In somecases, a protective hood laterally surrounds a periphery of thetransparent cover. The module also may include auto-focus components,each of which is disposed respectively over a corresponding one of thebeam shaping systems. A respective electrically conductive connectioncan be provided from each auto-focus component to a corresponding one ofthe printed circuit boards.

In another aspect, an optical module includes an image sensor on asubstrate. A beam shaping system is disposed over a photosensitiveregion of the image sensor. A spacer separates the beam shaping systemfrom the image sensor. The spacer includes an alignment edge in directcontact with a surface of the image sensor, and further includes anadhesion edge attached to the surface of the image sensor or to asurface of the substrate by adhesive.

The present disclosure also describes various methods for fabricatingthese and other optical modules. For example, in some implementations, awafer-level fabrication process can be used to make multiple opticalmodules at the same time.

In some implementations, the spacer portions are provided as a spacerwafer. The method also may include a separating step to form theplurality of optical modules.

Some implementations provide one or more of the following advantages.For example, by providing for focal length adjustment during thefabrication process, variations in the focal length from one channel toanother can be reduced. More generally, the focal length of each channelin a single-channel module or a multi-channel module can be made closerto the nominal focal length. Further, by providing a single transparentcover that extends across the entire array of image sensors (or otheractive optoelectronic components), thermal expansion and its associatedadverse consequences can be reduced. Some implementations can helpeliminate or reduce tilt in the optical channels. Some features can helpreduce the effects of stray light and optical cross-talk in the module.Further, various features can be provided to help protect wiring thatcouples the image sensors to the PCBs on which they are mounted, as wellas wiring that couples auto-focus components to the PCBs. The modulesand techniques described here can lead, for example, to array camerashaving improved image quality.

Some implementations include also one or more optical filters that aredesigned to allow only certain wavelength(s) of light (e.g., infra-red)to pass. In some cases, one or more optical filters can be placeddirectly on the optical assembly-side surface of the spacer. In otherinstances, the optical filter(s) may be integrated elsewhere within themodule.

Other aspects, features and advantages will be apparent from thefollowing detailed description, the accompanying drawings and theclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an example of a multi-channel module having a customizedspacer.

FIGS. 1A, 1B and 1C illustrate, respectively, a top cross-sectional viewand side cross-sectional views of a spacer for the implementation ofFIG. 1.

FIGS. 2A through 2D illustrate steps in accordance with a method offabricating a module with a customized spacer.

FIG. 3 is a flow chart of a fabrication technique for making a modulewith a customized spacer.

FIGS. 4A and 4B illustrate further details of a customized spacer.

FIG. 5 illustrates another example of a multi-channel module having acustomized spacer.

FIGS. 6A, 6B and 6C illustrate, respectively, a top cross-sectional viewand side cross-sectional views of a protective hood for theimplementation of FIG. 4.

FIGS. 7A and 7B illustrate an example of a customizable spacer for asingle channel module.

FIGS. 8A and 8B illustrate plan views of examples of customizablespacers.

FIGS. 9 and 9A illustrate another example of a customizable spacer for asingle channel module.

FIGS. 10A and 10B illustrate plan views of further examples ofcustomizable spacers.

FIGS. 11A-11N illustrate steps in a wafer-level fabrication process formaking multiple modules.

FIG. 12A illustrates a further example of a multi-channel module.

FIG. 12B illustrates a further example of a single channel module.

FIG. 13 is a flow chart of a method of assembling the module of FIG.12A.

FIG. 14 is a flow chart of a method of assembling the module of FIG.12B.

FIG. 15 illustrates an example of a module including features toeliminate or reduce tilt.

FIG. 16A illustrates an example of a spacer; FIG. 16B illustrates thespacer of FIG. 16A supporting an optical filter; FIG. 16C illustrates anoptical assembly attached to the spacer of FIG. 16B.

DETAILED DESCRIPTION

As shown, in FIG. 1, a module 20 for a compact array camera or otherimaging device includes multiple optical channels 22, 24, each of whichhas a respective beam shaping system such as a lens stack 26 held by alens barrel 28. The lens barrels 28 can be composed, for example, of aninjection molded epoxy material. In the illustrated example, each lensstack 26 includes multiple lens elements 30 stacked one over the otherand intersecting the optical axis of the particular channel 22, 24. Insome implementations, only a single beam shaping element (e.g., lens)may be provided for each optical channel. Each lens stack 26 issubstantially aligned with a respective monolithic image sensor 32,which can be implemented, for example, as a CCD or CMOS pixel array thatis operable to sense light (e.g., IR, visible, or UV) of a particularwavelength or range of wavelengths. Further, each image sensor 32, whichis an example of an active optoelectronic component, can be implementedas part of an integrated circuit (IC) formed, for example, as asemiconductor chip device that includes circuitry to perform processing(e.g., analog-to-digital processing) of signals produced by the lightsensing elements. In some implementations, each of the sensors 32 isoperable to sense light of the same wavelength or range of wavelengths,whereas in other implementations, the sensors 32 are operable to senselight at different wavelengths or ranges of wavelengths from oneanother. Using individual sensors 32, rather than a single large commonsensor for all the channels, can provide greater flexibility in choosingsensors with specific characteristics tailored for each particularchannel 22 or 24. Each sensor 32 can be mounted, for example, on arespective printed circuit board (PCB) 34. Wiring (i.e., electricallyconductive connections) 36 can be provided from each sensor 32 toelectrical contacts on the respective PCB 34. In some implementations,flip chip technology can be used to provide the electrical connectionsbetween the sensors 32 and the PCBs 34.

As further illustrated in the example of FIG. 1, the lens barrels 28 canbe mounted directly or indirectly on a transparent cover 38 that isdisposed between the lens stacks 26 and the sensors 32. The transparentcover 38 can be shaped, for example, as a plate whose thickness issubstantially uniform. The cover 38, which can protect the sensors 32from dirt and the like, is substantially transparent to thewavelength(s) of light detectable by the sensors 32. In some instances,the cover 38 is composed of a glass or plastic material. Providing asingle transparent cover 38 over all the sensors 32 can help improve themechanical stability of the module 20 and can help reduce the extent ofthermal expansion in the module. In some instances, the lens stack-sideof the cover 38, for example, can be partially coated with black chrome40 to prevent stray light from being received by the sensors 32. Theblack chrome 40 can be deposited on the surface of the cover 38 otherthan on areas corresponding to the optical channels 22, 24.

Each of the sensors 32 for the various channels 22, 24 can be positionedat a different respective distance from the transparent cover 38 (andthus from the respective lens stack 26). Thus, in the illustratedexample, the sensor 32 for the first channel 22 is closer to thetransparent cover 38 than the sensor 32 for the second channel 24. Toobtain this feature, a spacer 42 separates the transparent cover 38 fromthe sensors 32 and the PCBs 34. The upper surface of the spacer 42 canbe in contact with the sensor-side of the transparent cover 38, and thelower surface(s) of the spacer can be in contact with the upper surfacesof the sensors 32 and the PCBs 34.

As illustrated in the example of FIG. 1, the height of the spacer 42 inan area defining one of the optical channels 22, 24 can differ from theheight of the spacer in an area defining the other channel. Thus, in theillustrated example, the height of the spacer 42 is smaller for thefirst channel 22 than for the second channel 24. In particular, thedistance from the sensor-side of the transparent cover 38 to the sensor32 in the first channel 22 is h1, whereas the distance from thesensor-side of the transparent cover 38 to the sensor 32 in the secondchannel 24 is h2 (>h1). Likewise, the distance from the sensor-side ofthe transparent cover 38 to the PCB 34 in the first channel 22 is H1,whereas the distance from the sensor-side of the transparent cover 38 tothe PCB 34 in the second channel 24 is H2 (>H1). The difference in theheight of the spacer for the various channels 22, 24 can provide forfocal length correction during manufacture and assembly of the imagingdevice. For example, if (during fabrication and assembly) the respectivefocal lengths of the channels 22, 24 differ from a nominal value, theheight of the spacer 42 can be adjusted to correct for that difference.Thus, the actual focal length of each channel 22, 24 can substantiallymatch a desired or specified value by placing the sensors 32 for thevarious channels 22, 24 at different respective distances from thetransparent cover 38 (and thus from the respective lens stacks 26).Nevertheless, in some implementations, each of the sensors 32 may be atsubstantially the same distance from the transparent cover 38.

The spacer 42 also can include trenches 48 to provide space for theelectrical connections 36 from the sensors 32 to the PCBs 34. Thetrenches 48 can be formed as annular spaces (e.g., ring orrectangular/square shaped) such that the electrical connections 36 canbe provided along any part of the periphery of each respective sensor32. FIGS. 1A, 1B and 1C show, respectively, a top cross-sectional viewand side cross-sectional views of the spacer 42. The spacer 42 thuslaterally surrounds the electrical connections 36, thereby providing alevel of protection for them. The spacer 42 also laterally surroundseach of the image sensors 32 such that a portion of the spacer separateseach image sensor 32 from an adjacent image sensor 32.

As further illustrated in the example of FIG. 1, the spacer 42 can beformed as a single monolithic piece and can be composed, for example, ofa vacuum injection molded epoxy material that is substantially opaquefor the wavelength(s) of light detectable by the sensors 32. In somecases, the lens barrels 28 are composed of the same material as thespacer 42. The spacer has openings (i.e., through-holes) 46 that serveas light conduits of the channels 22, 24 to allow light to pass from thelens stacks 26 through the transparent cover 38 and to the respectivesensor 32. The sidewalls 42A and internal wall 42B of the spacer 42 thatextend from the transparent cover 38 to the surface of the PCBs 34laterally surround the sensors 32, thereby helping shield the sensorsfrom stray light and from optical cross-talk.

In some implementations, optical filters can be provided, for example,on the transparent cover 38 or on the image sensors 32. Various types ofoptical filters can be used, such as monochromatic, Bayer or other colorfilter arrays, neutral density, or infra-red (IR). Depending on theimplementation, the filters for each channel may be the same or maydiffer.

In some cases, the PCBs 34 are mounted on a common flexible cable (FPC)44, which provides electrical connections to the sensors 32. Theflexible cable 44 can conform to the different vertical positions of thePCBs 34.

Some implementations also include a protective hood 47 that surroundsthe periphery 49 of the transparent cover 38. The hood 47 can helpshield the module from stray light and can help conceal the transparentcover 38 from view. The hood 47 can include a top ledge 50 located overthe top surface of the transparent cover 38 near its periphery. The hood47, which can be formed, for example, of an injected molded epoxymaterial, should be substantially opaque to wavelength(s) of lightdetectable by the sensors 32. In some cases, the hood 47 is composed ofthe same material as the spacer 42. The top ledge 50 of the hood 47 canbe attached to the outer sidewalls of the lens barrels 28 and can reston the upper surface of the transparent cover 38.

Although the example of FIG. 1 illustrates a module 10 having twooptical channels, some implementations may include only a single opticalchannel. Other implementations may include a M×N array of opticalchannels, wherein one or both of M and N are two or more.

FIGS. 2A through 2D illustrate an example of fabricating portions of amodule 10 having a customized spacer that provides channel focal lengthadjustment (e.g., focal length correction). As illustrated in FIG. 2A,beam shaping systems, such as lens barrels 28 holding respective lensstacks 26, are attached to a first surface of a transparent plate 38. Aninitial spacer 102 is attached to a second surface on the opposite sideof the transparent plate 38. The initial spacer 102 can include openings46 for the light conduit of each channel. The initial spacer 102 alsocan include a first set of extensions 104 to provide sensor-edgefeatures for contact to image sensors and a second set of extensions 106to provide PCB-edge features for attachment to PCBs on which the imagesensors are mounted. The extensions 104, 106 extend in a direction awayfrom the plate 38. The initial spacer 102 can be formed, for example, bya vacuum injection molding and/or micromachining processes.

Before attaching the image sensor/PCB pairs to the spacer 42, a focallength (e.g., FFL) measurement is made for each optical channel (FIG. 3,block 202). The measured focal lengths then can be compared to aspecified (e.g., nominal) focal length value (block 204). If themeasured value for a particular optical channel differs from thespecified value, various adjustments can be made. In some cases,adjustments can be made to provide for FFL channel correction (block206). This can be accomplished, for example, by applying (e.g., byphotolithography) one or more layers of optically transparent materialto the underside of the transparent cover 38. The thickness of thelayer(s) provided for each optical channel may differ depending on theamount of correction needed for each channel. Further, the height of thespacer extensions 104, 106 for the particular channel can be adjusted toachieve a corrected focal length of the channel that substantiallymatches the desired value (block 208). For example, the height of someor all of the extensions 104, 106 can be reduced by micromachining. Theheight of the extensions 104, 106 for different channels may be reducedby the same amount or different amounts, depending on the amount offocal length correction to be made for each channel. No adjustment maybe needed for a particular channel if the focal length of the channelalready is satisfactory (i.e., within a specified tolerance of thenominal value). The result is a customized spacer 102A (see FIGS. 2B and2C) which provides focal length adjustment (e.g., correction) and hassensor-edge features 104A, 104B for contact with the upper surface ofthe respective image sensors 32 and PCB-edge features 106A, 106B forattachment to the upper surface of the respective PCBs 34. FIG. 2C showsan example in which the heights of the extensions 104A, 106A for theoptical channel on the left-hand side were adjusted, whereas the heightsof the extensions 104B, 106B for the optical channel on the right-handside were not adjusted. In the resulting customized spacer 102A, thevertical position (i.e., the height) of the sensor-edge feature 104A forone channel may differ from the vertical position of the sensor-edgefeature 104B of another channel. Likewise, the vertical position (i.e.,the height) of the corresponding PCB-edge feature 106A for one channelmay differ from the vertical position of the PCB-edge feature 106B ofanother channel. In some cases, the focal lengths for the channelssubsequently may be re-measured to confirm whether additionalmicromachining of the extensions 104, 106 is needed. In someimplementations, both steps 206 and 208 are performed; in other cases,only one of the steps 206, 208 may be performed, and the other may beomitted.

After making any necessary or desired adjustments to the spacer, thesensor-edge features 104A, 104B of the spacer 102A can be brought intocontact with respective image sensors 32 and the PCB-edge features 106A,106B of the spacer 102A can be attached (directly or indirectly) to therespective PCBs 34 on which the image sensors 32 are mounted (FIG. 3,block 210; see FIGS. 2C and 2D). In some cases, the upper surface ofeach PCB 34 is attached directly, for example, by an adhesive to arespective PCB-edge feature 106A, 106B. The wiring 36 connecting thesensors 32 to the PCBs 34 should be provided prior to attaching thesensor/PCB pairs to the spacer 102A. After attaching the spacer 102A tothe image sensors/PCB pairs, a protective hood 47 and flexible cable 44can be provided (see FIG. 1).

In some implementations, the height of the image sensors 32 may varyslightly from a nominal value or may vary with respect to one another.Likewise, the thickness of glue or other adhesive 33 that is used toattach the images sensors 32 to the respective PCBs 34 may vary from anominal value or may vary from one sensor/PCB pair to another. Thus,variations in the sensor-to-PCB thickness (D) may occur. See FIG. 4A. Toreduce the extent of any such variations, the height of the extension106 for a particular PCB-edge feature 106A should be such that, when thecorresponding sensor-edge feature 104A of the spacer is brought intocontact with the upper surface of the image sensor 32, there is a smallspace (of thickness (t)) between the PCB-edge feature 106A and thesurface of the PCB 34. In some cases, it may be necessary to reduce theheight of the extension 106, for example, by micromachining, prior tobringing the spacer into contact with the image sensor 32. The spacebetween the spacer's PCB-edge feature 106A and the PCB 34 then can befilled with an adhesive so that the PCB-edge feature 106A restsindirectly on the PCB 34. Thus, in this case, the PCB-edge feature 106Ais attached indirectly to the PCB 34. In this way, the focal lengthadjustment (e.g., correction) for a given channel need not be impactedsignificantly by any variations in the sensor-to-PCB thickness (D). SeeFIG. 4B. In particular, the foregoing techniques can accommodate fordifferences in the sensor-to-PCB thickness (D).

In some implementations, multiple modules like the module 20 can be madeby a wafer-level process. Wafer-level processes allow multiple modules20 to be fabricated at the same time. Generally, a wafer refers to asubstantially disk- or plate-like shaped item, its extension in onedirection (z-direction or vertical direction) is small with respect toits extension in the other two directions (x- and y-, or lateral,directions). In some implementations, the diameter of the wafer isbetween 5 cm and 40 cm, and can be, for example, between 10 cm and 31cm. The wafer may be cylindrical with a diameter, for example, of 2, 4,6, 8, or 12 inches, one inch being about 2.54 cm. In someimplementations of a wafer level process, there can be provisions for atleast ten modules in each lateral direction, and in some cases at leastthirty or even fifty or more modules in each lateral direction.

As an example of a wafer-level process, multiple beam shaping systemscan be arranged on one surface of a transparent wafer, and spacerportions can be provided on the sensor side of the transparent wafer.The transparent wafer can be composed, for example, of glass or plastic.The spacer portions can be provided, for example, by vacuum injectionmolding, or as a spacer wafer that is attached to the sensor-side of thetransparent wafer. The spacer wafer can be composed, for example, of anon-transparent material, such as a vacuum injected polymer material(e.g., epoxy, acrylate, polyurethane, or silicone) containing anon-transparent filler (e.g., carbon black, pigment, or dye). Aftermeasuring the focal length (e.g., FFL) for each optical channel, theheight of the spacer can be adjusted, for example, by micromachining, toprovide for focal length correction of one or more of the channels. Theimage sensors then can be brought into contact with the spacer portions,and the stack can be separated (e.g., by dicing) into multipleindividual modules 20. In some cases, the dicing may be performed priorto bringing the image sensors 32 into contact with the spacer portions.Further, in some cases, the dicing may be performed even beforemicromachining the spacer portions to provide for focal lengthcorrection.

In some implementations, other features can be included, such as anauto-focus feature. FIG. 5 illustrates an example of such animplementation. The module 300 of FIG. 5 is similar to the module 20 ofFIG. 1, but also includes auto-focus components 302 each of which isassociated with a respective one of the optical channels 22, 24. Theauto-focus components 302 can be disposed over the respective lens stack26 and can include, for example, a dynamic lens with electricalconnections to the PCB 34. In some implementations, the auto-focuscomponents include a lens that can be moved vertically within theoptical channel to modify the optical characteristics for the channel.The electrical connections from the auto-focus component 302 to the PCB34 can include, for example, an electrically conductive coating 304along the outer sides of the lens barrels 28. The electricallyconductive coating 304 can be formed, for example, as copper tracesalong the outer surfaces of the lens barrels 28. The conductive coating304 can be coupled directly to the auto-focus component 302 and towiring 306, which in turn is coupled to a respective one of the PCBs 34.Signals from the PCBs 34 thus can be provided to the auto-focuscomponents 302 to control and adjust their optical characteristics.

As shown in FIG. 5, a protective hood 47A surrounds the periphery 49 ofthe transparent cover 38 and also can help shield the module from straylight and can help conceal the transparent cover 38 from view. The hood47A can include a top ledge 50 located over the top surface of thetransparent cover 38 near its periphery. In addition, the hood 47A canprovide channels 308 for the wiring 306. FIGS. 6A, 6B and 6C illustrate,respectively, a cross-sectional top view and cross-sectional side viewsof the hood 47A.

As described above, customized spacers that include sensor-edge featuresfor contact with the upper surface of the respective image sensors, andthat include PCB-edge features for attachment to the upper surface ofthe respective PCBs, can facilitate focal length adjustment (e.g., FFLcorrection). Customized spacers also can be used to address other issuesthat may arise during fabrication of modules that incorporate an activeoptoelectronic component (e.g., an image sensor). The followingparagraphs describe examples of modules including a customized spacerthat can help address such other problems that sometimes arise duringfabrication.

Tilt, for example, can be introduced as a result of the unevendistribution of adhesive used to attach a beam shaping system (e.g., alens barrel and optical assembly) to a transparent wafer, or as a resultof the uneven distribution of adhesive used to attach an opticalassembly to an image sensor or PCB substrate. The tilt can cause poorimage quality. Further, if the adhesive is not controlled properly, itmay migrate to an active portion of the image sensor, and render thesensor unusable. Customized spacers can be used to help reduce theoccurrence of tilt of components in the module, and/or to help preventadhesive from migrating to active portions of the image sensor.

As shown in FIG. 7A, a beam shaping system 425 (e.g., optics assembly426 and lens barrel 428) is at one side (i.e., the object-side) of atransparent plate 438, and a spacer 402 is at the second side (i.e., thesensor-side) of the transparent plate 438. The lens barrel 428 can beattached to the spacer 402 by adhesive or may be formed as a unitarypiece with the spacer 402. In some instances, an optical element such asan optical filter 440 may be present on the transparent plate 438. Asillustrated in FIG. 7A, the spacer 402 includes a through-holesubstantially aligned with the beam shaping system and corresponding toan optical channel. The spacer 402 further includes a first extensionthat provides a sensor alignment edge 404, and a second extension thatprovides a PCB adhesion edge 406. The sensor alignment edge 404 definesthe distance from the upper surface of the image sensor 432 to theoptical assembly 426 (see FIG. 7B). The PCB adhesion edge 406 providesthe bond line (i.e., the location where adhesive is placed forattachment to the PCB 434).

The sensor alignment edge 404 can be customized (e.g., machined) suchthat the focal length and any tilt are corrected. As shown in FIG. 7B,the alignment edge 404 is placed in direct contact with an inactiveportion of the image sensor 432 (e.g., near the periphery of the sensor432). Preferably, no adhesive is used between the alignment edge 404 andthe surface of the sensor 432. The PCB adhesion edge 406 also can becustomized (e.g., machined) such that it is allows the alignment edge404 to make contact with the upper surface of the image sensor 432, andalso allows for adhesive (e.g., at a thickness of approximately 20 μm±5to 10 μm) to be present between the adhesion edge 406 and the uppersurface of the PCB 434 (see FIG. 7B).

The customized spacer 402 can provide various advantages in someimplementations. For example, the adhesive 410 can be kept away moreeasily from the image sensor 432. Further, the wires 412 connecting thesensor 432 to the PCB 434 can be better protected because they aredisposed within a cavity 411 between the alignment and adhesion edges404, 406. Also, better control of the height/tilt can be achieved insome cases because the adhesive is on the PCB adhesion edge 406, not thesensor alignment edge 404.

The alignment edge 404 can take any one of various forms. For example,as shown in FIG. 8A, the sensor alignment edge 404 laterally cansurround the entire periphery of the active (i.e., photosensitive)portion 433 of the image sensor 432. In other implementations, thesensor alignment edge 404 can be implemented as a plurality ofindividual pillars (see FIG. 8B). Preferably, there are at least threesuch pillars to provide mechanical stability.

In some implementations, the inactive area of the image sensor 432 maybe sufficiently large as to be capable of accommodating both an adhesionedge 406A as well as an alignment edge 404 (see FIG. 9). In that case,the adhesion edge 406A can be attached (e.g., by adhesive) to theinactive area of the sensor 432; likewise, the alignment edge 404 can beplaced in direct contact with the inactive area of the sensor 432 (i.e.,without adhesive). Prior to attaching the spacer 402A to the imagesensor 432, one or both of the alignment and adhesion edges 404, 406Acan be machined to the desired dimensions. As shown in the magnified,cut-away view of FIG. 9A, the cavity 411 between the edges 404, 406A canbe designed so that capillary forces wick away the adhesive (e.g.,epoxy) such that it does not reach the sensor alignment edge 404 and theactive area of the image sensor 432. In some cases, the conductive wires412 connecting the sensor 432 to the PCB 434 can be encapsulated (e.g.,with back-fill epoxy) to enhance their mechanical stability. Thepresence of the adhesive 410 reduces the risk that the encapsulantcovering the wires 412 will contaminate the image sensor 432.

In some implementations, the adhesive 410 may be present alongsubstantially the entire contact surface of the adhesive edge 406A. Inother cases, the adhesive may be present only on parts of the edge 406,406A. For example, individual beads of adhesive 410 may be provided onportions of the edge's contact surface (see FIG. 10A). To reduce theoverall footprint of the spacer 402, 402A, the sensor alignment edge 404and the sensor adhesive edge 406A can share a side 444 in common (seeFIG. 10B). In that case, adhesive 410 can be placed along the othersides of the sensor adhesive edge 406, 406A, but would not be placedalong the side 444 shared in common with the sensor alignment edge.

In the foregoing implementations, the optics assembly 426 can include,for example, a stack of lenses that provides a single optical channel,or a stack of lens arrays that provides two or more optical channels. Inthe case of lens arrays, some of the arrays may be implemented aslaterally contiguous monolithic arrays that span across multiplechannels.

FIGS. 11A-11N illustrate an example of a wafer-level process forfabricating assemblies that include customized spacers having anadhesion edge and an alignment edge. As shown in FIG. 11A, a transparentwafer 1102 (e.g., composed of glass or plastic) is attached to UV dicingtape 1104. In some cases, the wafer 1102 may be pre-coated with anoptical filter or other layer. The transparent wafer 1102 is separated,for example by dicing, into individual transparent covers 1106, as shownin FIG. 11B. Next, as illustrated by FIG. 11C, vacuum injection tools1108, 1110 are provided such that the lower tool 1110 is flush with thebottom of the transparent covers 1106, and the upper tool 1108 hascavities 1112 that define the spacer regions. Then, as shown in FIG.11D, a non-transparent material, such as a polymer material (e.g.,epoxy, acrylate, polyurethane, or silicone) containing a non-transparentfiller (e.g., carbon black, pigment, or dye), is injected under vacuuminto the regions between the tools 1108, 1110. Subsequently, thenon-transparent material 1114 that fills the cavities 1112 is cured, forexample, using UV radiation (FIG. 11E). The tools 1108, 1110 then areremoved from the resulting structure 1115 (see FIG. 11F).

Next, as shown in FIG. 11G, a respective beam shaping system 1116 isattached, for example by adhesive, to each transparent cover 1106 or tothe upper surface of the non-transparent material 1114. Each beamshaping system 1116 can include, for example, a lens stack and lensbarrel. Alternatively, a beam shaping system for the optical channelsmay be provided in the form of a lens wafer (e.g., a non-transparentsubstrate with an array of through holes filled with transparentmaterial forming optical elements), or by lens elements individuallyplaced or replicated directly onto a cover glass. Various measurementscan be made for each optical channel, including the channel's modulationtransfer function (MTF), the channels' focal length and/or the amount oftilt with respect to a reference plane. As illustrated by FIG. 11H, themeasurements may involve generating one or more optical signals 1117that pass through the optical channel, and measuring one or moreparameters of the signal(s). In some implementations, the opticalmeasurements are performed at a later stage in the process (e.g., justprior to the machining depicted in FIG. 11M). The measurements can beused in subsequent processing steps to machine the spacer. Regardless ofwhether the optical measurements are performed immediately following thestep of FIG. 11G or at a later stage, another vacuum injection tool 1118is provided (see FIG. 11I), and non-transparent material 1120 isinjected under vacuum for the alignment and adhesion edges of eachchannel (see FIG. 11J). Here too, the non-transparent material can be apolymer material (e.g., epoxy, acrylate, polyurethane, or silicone)containing a non-transparent filler (e.g., carbon black, pigment, ordye). The non-transparent material is cured, for example, UV radiation(FIG. 11K), and the resulting structure 1121 is removed from the tool1118 (FIG. 11L). As indicated by FIG. 11M, the alignment and adhesionedges then can be micro-machined, as needed, based on the distance froma reference plane 1122 and the previously-made optical measurements. Asshown in FIG. 11N, the resulting structure then can be separated (e.g.,by dicing) along vertical lines 1124 into individual modules or arraysof modules, each of which includes a customized spacer having alignmentand adhesion edges as described above. Each diced module then can beplaced, for example, on an individual image sensor substrate structure.

In some cases, prior to dicing, the module wafer resulting from thecompletion of the steps depicted in FIG. 11M may be attached (e.g., byadhesive) to a substrate wafer (e.g., a PCB wafer) on which are mountedan array of sensors. The resulting structure then can be diced intoindividual modules or arrays of modules.

In the foregoing examples, the adhesive (e.g., 410) for attaching theoptical assembly to the PCB (e.g., 434) is disposed primarily betweenadhesion edges (e.g., 406) on a sensor-side of the spacer (e.g., 402)and an upper surface of the PCB 434. In some implementations, however,the adhesion edges can be provided at side surfaces laterally encirclingthe side edges of the transparent plate/cover 438. Examples areillustrated in FIGS. 12A and 12B.

As shown, for example, in FIG. 12A, a multi-channel module includes atransparent cover 438 laterally surrounded by material 446 that issubstantially opaque for the wavelength(s) of light detectable by theactive region 433 of the image sensor 432. The material 446 can becomposed, for example, of a vacuum injection molded epoxy and can helpprevent stray light from impinging on the active regions of the sensor432. In some cases, the material 446 laterally surrounding the cover 438is the same as the material forming the spacer 402 (including thealignment edges 404) and/or the lens barrels 428. As further illustratedin the example of FIG. 12A, the transparent cover 438 may be embeddedwithin the surrounding material 446. As described in connection with theexample of FIG. 7B, the sensor alignment edges 404 can be in directcontact with the non-active regions of the sensor 432 and establish apredetermined fixed distance between the sensor 432 and the transparentcover 438. Adhesion edges 406B can be provided at the outer sidesurfaces 406B of the vacuum injection molded epoxy material 446encircling the transparent cover 438. The outer side surface definingthe adhesion edge(s) 406B can be substantially perpendicular to thesurface of the substrate 434. As shown in FIG. 12A, adhesive 410 holdsthe optics assembly in place over the sensor 432. In this case, theadhesive, which can be a high viscosity material, is in contact with theadhesion edges 406B as well as the sensor-side surface of the PCB 434.The example of FIG. 12A also includes FFL correction layers 448, whichcan be used during fabrication of the modules to adjust the focallengths of the channels.

FIG. 12B illustrates an example of a single channel module, which alsohas adhesion edges 406B similar to those described in connection withFIG. 12A.

In many cases, for the implementations of FIGS. 12A and 12B, it is notnecessary to machine the PCB adhesion edges 406B. Thus, in some cases,the process for fabricating modules using the arrangement of FIGS. 12A,12B can be simplified.

Techniques for assembling the modules depicted in FIGS. 12A and 12B aredescribed next. For example, with respect to the multi-channel module ofFIG. 12A, an assembly 450 is provided and includes the lens stacks 426,lens barrels 428, transparent cover 438, spacer 442 and the material 446encircling the cover 438. The focal lengths of the respective channelsof the assembly are measured (1302 in FIG. 13), and based on themeasurements, the thickness of one or both FFL correction layers 448 maybe adjusted such that the focal lengths of the channels aresubstantially the same (1304). In some cases, the alignment edges 404may be machined such that the focal lengths of the respective channelsare focused on the active region 433 of the sensor 432 (1306).High-viscosity adhesive 410 then is injected onto the periphery of thePCB 434 so as to encircle the sensor 432 (1308). Next, the assembly 450is brought into contact with the sensor 432 (via the alignment edges404) (1310). During this latter process, some adhesive 410 is forcedunder the adhesion edges 406B, with the result that the adhesive 410 maypartially encase the electrical connections 436. The adhesive then iscured, for example, using heat, UV or both (1312). In some cases, thecured adhesive 410 is non-transparent to wavelengths of light detectableby the sensor 432.

To assemble the single-channel module of FIG. 12B, an assembly 452 isprovided and includes the lens stacks 426, lens barrels 428, transparentcover 438, spacer 442 and the material 446 encircling the cover 438. Thefocal length of the channel is measured (1402 in FIG. 14). In somecases, the alignment edges 404 may be machined such that the focallength of the channel is focused on the active region 433 of the sensor432 (1404). Next, high-viscosity adhesive 410 is injected onto theperiphery of the PCB 434 so as to encircle the sensor 432 (1406). Theassembly 452 then is brought into contact with the sensor 432 (via thealignment edges 404) (1408). During this latter process, some adhesive410 is forced under the adhesion edges 406B with the result that theadhesive 410 may partially encase the electrical connections 436. Theadhesive 410 then is cured, for example, using heat, UV or both (1410).In some cases, the cured adhesive 410 is non-transparent to wavelengthsof light detectable by the sensor 432.

In some cases, tilt correction can be addressed in other ways either inaddition to, or as an alternative to, the techniques discussed above.For example, in some instances, an optics assembly (e.g., a lens stack)is placed within a lens barrel that is attached, by adhesive, to atransparent plate over the photosensitive part of the image sensor.Unevenness in the adhesive can result in misalignment of the lens barrelsuch that the lenses are tilted relative to the plane of the imagesensor. The tilt, in turn, may result in poor image quality. To helpeliminate or reduce the impact of the uneven adhesive, one or more(e.g., three) projections 502 can be provided on the sensor-side of alens array 504 (see FIG. 15). The projections 502 can be formed, forexample, during the same injection molding process used to form the lensarray 504. When the lens array 504 is placed into the lens barrel 506,the projection(s) 502 extend beyond the bottom of the lens barrel 506.The projection(s) 502 rest directly on the transparent cover 508 so asto define a fixed distance between the image sensor 510 and the lensarray 504, whereas the lens barrel 506 is attached to the transparentcover 508 by adhesive 512. In some cases, instead of multipleprojections 502, a single projection in the form of a continuous edgeextends from the sensor-side of the lens array and is attached to thetransparent cover 508. Any unevenness in the adhesive 512 between thelens barrel 506 and the transparent cover 508 will not result in tilt ofthe lens array 504. As in the other implementations described above, thetransparent cover 508 can be surrounded laterally by a non-transparentspacer 514 that provides a fixed distance between the image sensor 510and the transparent cover 508. The image sensor 510 can be mounted on aPCB or other substrate 516.

As described above, the foregoing examples of modules include atransparent cover or plate (e.g., transparent cover 38) disposed betweenthe lens stacks and the image sensor(s). However, in some cases, it canbe desirable to omit such a transparent cover or plate, for example, soas to achieve a reduction in the overall height of the module. Asdescribed above, the spacer itself (e.g., 42) can include one or moreopenings (e.g., 46) that allow light to pass, between the opticalassemblies (e.g., 28) and the optoelectronic components (e.g., the imagesensors 32).

The sensor-side of the spacer can be designed in accordance with any ofthe implementations previously described, and can include a first set ofextensions (e.g., 104) to provide sensor-edge features for contact tothe image sensor(s) and a second set of extensions (e.g., 106) toprovide PCB-edge features for attachment to PCB(s) on which each imagesensor is mounted.

As previously described, an optical filter can be integrated into themodule to allow only light of a selected wavelength (or within a narrowwavelength range) to pass. In some implementations, an optical filtercan be placed directly on the optical assembly-side surface of thespacer. FIG. 16A illustrates an example of such a spacer 38A, whichincludes at least one opening 602. The spacer 38A can be formed, forexample, by vacuum injection molding. In some cases, the optical filtermay be designed to allow, for example, only infra-red (IR) radiation topass. The filter also may include an anti-reflective coating.

In the illustrated example, the optical assembly-side surface of thespacer 38A is designed to receive a thin-film optical filter 604 (seeFIGS. 16A and 16B). The filter 604 can be implemented, for example, as afoil having a thickness on the order of about 100 μm or otherappropriate thickness. In such cases, the optical assembly-side of thespacer 38A can have an indented surface 606 (see FIG. 16) shaped andsized to receive and hold the filter 604. The opening 602 is disposed inthe middle of the region defining the indented surface. Formulti-channel implementations, the spacer 38A can support two or morefilters (a filter for each channel) on the optical assembly-sidesurface. In such cases, filters having different optical characteristicsfrom one another may be provided for the various channels. Duringfabrication of the modules (e.g., in a wafer-level process), the eachfilter 604 is placed onto the optical assembly-side surface of thespacer 38A. In other cases, an optical filter may be disposed elsewherewithin the module, such as within the optical assembly or on the imagesensor, or it may be integrated into the sensor's micro-lens array. Inother implementations, the module may not include a filter at all.

Regardless of whether a filter 604 is placed on the spacer 38A, theoptical assembly (including, e.g., an injected molded lens stack) can beattached directly to the spacer, for example, by epoxy or anotheradhesive (see FIG. 16C).

The modules described here can be used, for example, as compact digitalcameras that can be integrated into various types of consumerelectronics and other devices such as mobile phones, smart phones,personal digital assistants (PDAs) and laptops.

Although the illustrated examples are described in the context ofimaging devices that include image sensors, other implementations mayinclude different types of active optoelectronic components, includinglight emitters (e.g., light emitting diodes (LEDs), infra-red (IR) LEDs,organic LEDs (OLEDs), infra-red (IR) lasers or vertical cavity surfaceemitting lasers (VCSELs)). In this case, the transparent covers (ifpresent) should be substantially transparent to the wavelength(s) oflight emitted by the active optoelectronic components.

Some or all of the foregoing features may not be present in someimplementations. Further, various features described in connection withdifferent ones of the foregoing examples can be combined in a singleimplementation. Also, various modifications within the spirit of theinvention will be readily apparent to one of ordinary skill.Accordingly, other implementations are within the scope of the claims.

1. An optical module comprising: a plurality of active optoelectroniccomponents each of which is mounted on a respective printed circuitboard, wherein each of the active optoelectronic components isassociated with a respective different optical channel; a plurality ofoptical assemblies, each of which is substantially aligned over adifferent respective one of the optical channels; and a spacerseparating the active optoelectronic components and printed circuitboards from the optical assemblies, wherein the optical assemblies areattached by adhesive directly to an optical assembly-side surface of thespacer, and wherein a first one of the active optoelectronic componentsis separated, by the spacer, from a first one of the optical assembliesby a first distance and wherein a second one of the activeoptoelectronic components is separated, by the spacer, from a second oneof the optical assemblies by a different second distance.
 2. The opticalmodule of claim 1 wherein the spacer includes first edge features incontact with top surfaces of the active optoelectronic components andsecond edge features attached to top surfaces of the printed circuitboards.
 3. The optical module of claim 2 wherein the second edgefeatures are attached to the top surfaces of the printed circuit boardsby adhesive.
 4. The optical module of claim 1 wherein the spacer is asingle monolithic piece.
 5. The optical module of claim 1 wherein thespacer has trenches that provide space for electrical connections fromthe active optoelectronic components to the printed circuit boards. 6.The optical module of claim 4 wherein the trenches are formed as spacesabout a periphery of each respective active optoelectronic component. 7.The optical module of claim 1 wherein the active optoelectroniccomponents comprise image sensors, and wherein each of the opticalassemblies is aligned over a respective one of the image sensors.
 8. Theoptical module of claim 7 wherein the spacer has through-holes each ofwhich allows light to pass from a respective one of the opticalassemblies to a respective one of the image sensors.
 9. The opticalmodule of claim 8 further including at least one optical filtersupported by the optical assembly-side surface of the spacer.
 10. Theoptical module of claim 9 wherein each optical filter is disposed over arespective one of the through-holes of the spacer.
 11. The opticalmodule of claim 1 further including at least one optical filtersupported by the optical assembly-side surface of the spacer.
 12. Theoptical module of claim 1 wherein the optical assembly-side surface ofthe spacer includes an indented region shaped and sized to receive anoptical filter.
 13. A method of fabricating an optical module, themethod comprising: providing a spacer plate including respectivethrough-holes each of which corresponds to a respective optical channel,the spacer further including first extensions to provide respectivesensor-edge features for contact with respective image sensors andsecond extensions to provide respective PCB-edge features for attachmentto respective PCBs, the first and second extensions being present on afirst side of the spacer; modifying a height of one or more of theextensions to adjust for at least one of a focal length or tilt of atleast one of the optical channels; subsequently bringing respectiveactive optoelectronic components into contact with respective ones ofthe sensor-edge features, and attaching respective PCBs on which therespective active optoelectronic components are mounted to respectiveones of the PCB-edge features; the method further including attachingoptical assemblies by adhesive directly to a second side of the spacer,the second side of the spacer being on an opposite side of the spacerfrom the first side.
 14. The method of claim 13 further including:measuring a respective focal length for each of the optical channels;and comparing each of the measured focal lengths to a specified value;wherein modifying a height of one or more of the extensions is based onthe comparing.
 15. The method of 13 wherein modifying the height of oneor more of the extensions includes micromachining one or more of theextensions to reduce its height.
 16. The method of claim 13 wherein eachrespective PCB is attached to a respective one of the PCB-edge featuresvia adhesive.
 17. The method of claim 13 further including placing anoptical filter on the second side of the spacer such that the opticalfilter is supported by the spacer and covers one of the through-holes ofthe spacer.